1. VIRUSES, BACTERIA, and PRIONS
VIRUSES, BACTERIA, and PRIONS

2. VIRUSES Tiny: smaller than ribosomes

3. VIRUSES Contain DNA or RNA SINGLE or DOUBLE stranded
NUCLEIC ACID surrounded by PROTEIN coat = CAPSID
Some have ENVELOPE outside capsid

4. BACTERIOPHAGES =viruses that infect bacteria
no cellular machinery of their own Can only reproduce in host cells

5. HIV (Human Immunodeficiency Virus) AIDS virus
RETROVIRUS (Contains RNA)
Infects WHITE BLOOD CELLS
Has REVERSE TRANSCRIPTASE Enzyme that can use RNA to make DNA

7. PRIONS
“Misshaped” proteins
Change the shape of other proteins they contact
Aggregates of proteins accumulate in brain

8. PRIONS
Aggregates of proteins accumulate in brain
Neurological disorders
SCRAPIE in sheep
BOVINE SPONGIFORM ENCEPHALOPATHY (BSE) = “Mad Cow” disease
CHRONIC WASTING DISEASE
KURU
CREUTZFELD-JAKOB

9. Bacteria
Slide show by Kim Foglia (modified) Blue edged slides are Kim’s

10. Bacteria Bacteria review one-celled prokaryotes reproduce by mitosis
binary fission
rapid growth
generation every ~20 minutes
108 (100 million) colony overnight!
dominant form of life on Earth
incredibly diverse

11. How have these little guys gotten to be so diverse??
Bacterial genome
Single circular chromosome
haploid
naked DNA
no histone proteins
~4 million base pairs
~4300 genes
1/1000 DNA in eukaryote
Genome = all the DNA of an organism
Eukaryotes
• 1000 times more DNA
• only 10 times more genes
- introns, spacers, inefficiency
How have these little guys gotten to be so diverse??

12. Binary fission Replication of bacterial chromosome
Asexual reproduction
offspring genetically identical to parent
where does variation come from?

13. Variation in bacteria Sources of variation spontaneous mutation
transformation
plasmids
DNA fragments
transduction
conjugation
transposons
bacteria shedding DNA

14. Spontaneous mutation
Spontaneous mutation is a significant source of variation in rapidly reproducing species
Example: E. coli
human colon (large intestines)
2 x 1010 (billion) new E. coli each day!
spontaneous mutations
for 1 gene, only ~1 mutation in 10 million replications
each day, ~2,000 bacteria develop mutation in that gene
but consider all 4300 genes, then: 4300 x 2000 = 9 million mutations per day per human host!

15. Transformation Bacteria are opportunists
promiscuous!?
Bacteria are opportunists
pick up naked foreign DNA wherever it may be hanging out
have surface transport proteins that are specialized for the uptake of naked DNA
import bits of chromosomes from other bacteria
incorporate the DNA bits into their own chromosome
express new genes
transformation
form of recombination
mix heat-killed pathogenic & non-pathogenic
bacteria
While E. coli lacks this specialized mechanism, it can be induced to take up small pieces of DNA if cultured in a medium with a relatively high concentration of calcium ions.
In biotechnology, this technique has been used to introduce foreign DNA into E. coli.
mice die

16. Plasmids Small supplemental circles of DNA carry extra genes
,000 base pairs
self-replicating
carry extra genes
2-30 genes
genes for antibiotic resistance
can be exchanged between bacteria
bacterial sex!!
rapid evolution
can be imported from environment
Mini-chromosomes

17. Genes for antibiotic resistance = R Plasmids
Role in rapid evolution
Method for spreading “antibiotic resistance”

18. Plasmids & antibiotic resistance
Resistance is futile?
1st recognized in 1950s in Japan
bacterial dysentery not responding to antibiotics
worldwide problem now
resistant genes are on plasmids that are swapped between bacteria

19. TRANSDUCTION with viruses
Phage viruses carry bacterial genes from one host to another

20. Conjugation - Bacteria “sex”
Animation
Direct transfer of DNA between 2 bacterial cells that are temporarily joined
results from presence of F (fertility) plasmid
“male” extends sex pilli and attaches to “female” bacterium
cytoplasmic bridge allows transfer of DNA

21. TRANSPOSONS (Transposable elements)
“Jumping” genes
Can move from one place to another
1st described by Barbara McClintock in corn
Can move genes to new site